Astronomy

If Earth completely cleared its neighborhood there wouldn't be any fear of an asteroid hitting earth. I didn't know there were five dwarf planets: Ceres, Eris, Pluto, Makemake, and Haumea. I hadn't even heard of the other three. Why isn't Pluto's largest moon Charon included in the list of dwarf planets? They are tidally bound and similar in size that they could be said to be orbiting each other as they orbit the sun. The idea of a lost planet or two way out there that we haven't found is also interesting.

I believe Pluto's large moon is classed as well a moon. Your comment highlights the ludicrous nature of the definition of a planet. Pluto-Charon is a new phenomena as far as I know. We have seen it before in suns that are locked together in other galaxies, and sometimes planets going round one of the double stars is thrown over to going round the other. I saw a post on this in Astronomy Now a year or two ago. If that is not having an "uncleared orbit" I don't know what is! IAS is still very bound to a solar-centric view of the universe. There may even be more dwarf planets in orbit around Pluto.

I also agree that the possibility of a large planet going around the sun is intriguing. Pluto takes 3-and-a-half centuries to make one circuit the sun. How long would an even more remote planet/dwarf planet take?

We should know what those whit spots are on Ceres are within the next few days when Dawn goes into orbit around Ceres.

The Dawn Probe has ion propulsion, so it can use it as a brake to slow it down such that it can be gently captured into Ceres orbit. Then it will stay in orbit for a period to examine Ceres more closely.

That electric, ion propulsion is interesting. From the link you provided it can make a space craft go ten times faster than chemical propulsion using energy from the sun. I wonder why xenon is used and not some other element? Also I wonder if there is a way to harvest elements in space or around atmospheres of planets to replenish the xenon?

Xenon is an inert gas, like Helium and Neon, but heavier. Maybe it's used because it will not react with any of the materials in the spaceship, (e.g., it will not explode like hydrogen and oxygen!) Because it's heavier you can store a greater mass in your fuel container. Anyway, I'm jut guessing - get googling or ask on physics forum.

I did find that the fuel has to be easy to ionize and have a high mass/ionization ratio (that doesn't make sense to me) along with the contamination issue. Any material could be used as a propellant.

http://en.wikipedia.org/wiki/Ion_thruster#Propellants

I plan to observe Leo constellation. It is most visible from the late March, through April and May. This constellation seems interesting to me. :)

Back in the 1980s, at least, liquid metals were being considered as sources of ions for thrusters. I'm not sure what the situation is today. You would get gallium, or some other metal, to flow along a tungsten needle and generate ions coming off at the point using an electromagnetic field that would then keep the metal-gas ions in line and get them moving at speed. One would think it would be easier to mine metals than extract Xenon from (say) Jupiter's atmosphere, and they would (surely) be easier to store. Check out "liquid metal ion sources" of you want to read up on this.

Based on the Google Sky Map, both the moon and Jupiter are near Leo. I have only identified Algieba and Regulus in Leo while watching Jupiter. I should be able to see Denebola if the sky is clear enough.

Xenon is supposedly hard to get, but it is apparently easy to ionize. From the article argon is more common. I like the idea of getting energy from the sun and atoms from the atmosphere of the planets one visits for these space probes.

Last night I saw Orion constellation. It is easily recognized by its three bright stars close to each other called 'Orion's belt'.

I don't really know either how ion propulsion works, so join the club…
:)
Dawn is getting really close to Ceres, now some 35,000 miles, and retro- ion propulsion is slowing down a bit more. It should enter orbit around Ceres in a couple of days (March 6). I understand that it will be orbiting Ceres but starting on its dark side so we will not get any pictures or other images, until Dawn re-emerges on the other side into the sunlight. The following website is the one to watch for future info: http://dawn.jpl.nasa.gov/mission/status.asp. The two white spots that are so intriguing are seen on the image at the above link and there is a third image on the far left near the edge of the screen. There may even be others.

Ion propulsion works slowly, takes weeks to build up in space, so is useless for launching to escape velocity, but perfect for the delicate operation of going into orbit around Ceres.

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Originally Posted by free

Last night I saw Orion constellation. It is easily recognized by its three bright stars close to each other called 'Orion's belt'.

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Alnitak, Alniram, and Mintaka - I used to memorise such things when I was 12 :) Just below the belt is the famous Orion Nebula. It's a "fuzziness" that can be seen by the very sharp eyed, and should be obvious in binoculars. It's a vast cloud of gas from which stars are forming as you look - the closest region of massive star formation to Earth.

Might be a good place to send our ion powered robotic self-reproducing spacecraft on their first journey to the stars. Lots of material floating around for them to use!

Orion is a fascinating constellation - it also has two of the top ten brightest stars in the sky. One is Betelgeuse a red supergiant, on the top left shoulder. The other is Rigel at bottom right leg - a blue-white supergiant.

I agree about Orion constellation, it is very easy to identify by the three stars in a line and the two stars you identify: Betelgeuse and Rigel. Orion is the hunter and its easy to see the Hunter with her bow.

The link for the Dawn mission called Vesta a "giant asteroid". With Ceres being a "dwarf planet", there must be something that distinguishes these two names. Why is one a dwarf planet and the other a giant asteroid?

I think that a dwarf planet is round, planet-shaped, while an asteroid of any size is not.

It isn't very round, but Vesta apparently went through differentiation where the interior heated up and heavy elements sank while lighter elements rose to the surface.

In this video, there is a suggestion that it should be classified as the smallest "terrestrial planet". I also found it interesting that Jupiter's gravity stopped the rest of the asteroids from joining together. It "stirred them up" somehow. http://www.space.com/13902-vesta-ast...rf-planet.html